Timepieces of this type are known from the prior art. By way of example, EP Patent Application No. 0 786 685, filed on 16th Jan. 1997 in the name of SMH Management Services AG, discloses a timepiece comprising a device displaying a coloured decorative pattern. This document implements an optical valve located between a film on which the decorative pattern is printed and the timepiece crystal. When the optical valve is not being supplied with electrical energy, it appears black whereas when it is being powered, it becomes transparent thus making the decorative pattern visible.
This system has, however, a certain number of drawbacks, including in particular high manufacturing cost. The optical valve is preferably made in the form in a liquid crystal cell carrying transparent electrodes on each of its main faces for polarising the liquid crystals. Thus, deposition of the electrodes on the cell faces requires a method whose cost is not negligible, in particular if the optical system is to be implemented in a device for the general public at a low cost price. Moreover, this optical system is very complex in terms of electrical connections as regards the electrical powering of the liquid crystal control electrodes.